1. Fields of the Invention
This invention is directed to a variable venturi carburetor which is adapted on an internal combustion engine, more particulary to a variable venturi carburetor of the down-draught induction type which supplies a homogeneous fuel-air mixture to the engine over the wide range of changing engine conditions.
2. Description of the Prior Art
A motor vehicle is seldom operated in the restricted engine operation range, and therefore the carburetor adapted on the motor vehicle is required to constantly supply a correct fuel-air ratio depending upon the engine RPM and load conditions throughout the entire engine operational range. In prior carburetors, irrespective of whether including a fixed venturi or variable venturi, additional amounts of fuel or rich fuel-air mixture required for moving off or rapidly accelerating the vehicle will not be sucked up from a single fuel dispensing orifice, since at the time of moving off or rapid acceleration there will be sudden opening of a throttle valve or the like member which allows the additional amounts of air to inflow at such a lower velocity as to fail to draw additional amounts of fuel required for raising the engine speed. To this end, most prior devices must rely on a certain acceleration system included therein which provides an extra fuel supply to boost the normal fuel flow. However, such acceleration system has, for example, an additional fuel storage chamber or an injection pump, which is rather complicated and therefore would require frequent maintenance, adjustments and repairs. Also, these acceleration systems are controlled only by the accelerator pedal and not by the demand of the engine, such that over amounts of fuel than is needed for a particular engine operation would be produced and fed to the engine, resulting in the waste of the fuel and failing to efficiently raise the engine speed. That is, there have not been provided a carburetor of the type which is capable of compensating the over-depression of the accelerator pedal in order to supply correct amounts of fuel for acceleration purposes. Further, the prior carburetors have been provided with the choke valve for temporarily supplying a very rich mixture at the time of engine starting. The choke valve included in the carburetor adds the complexity to the latter in manufacturing and maintenance, and therefore has been desired to be removed.